1 files changed, 56 insertions, 0 deletions
diff --git a/absl/flags/usage.cc b/absl/flags/usage.cc
new file mode 100644
index 000000000000..4c01f5101291
--- /dev/null
+++ b/absl/flags/usage.cc
@@ -0,0 +1,56 @@
+//
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#include "absl/flags/usage.h"
+
+#include <string>
+
+#include "absl/flags/internal/usage.h"
+#include "absl/synchronization/mutex.h"
+
+namespace absl {
+namespace flags_internal {
+namespace {
+ABSL_CONST_INIT absl::Mutex usage_message_guard(absl::kConstInit);
+ABSL_CONST_INIT std::string* program_usage_message
+    GUARDED_BY(usage_message_guard) = nullptr;
+}  // namespace
+}  // namespace flags_internal
+
+// --------------------------------------------------------------------
+// Sets the "usage" message to be used by help reporting routines.
+void SetProgramUsageMessage(absl::string_view new_usage_message) {
+  absl::MutexLock l(&flags_internal::usage_message_guard);
+
+  if (flags_internal::program_usage_message != nullptr) {
+    ABSL_INTERNAL_LOG(FATAL, "SetProgramUsageMessage() called twice.");
+    std::exit(1);
+  }
+
+  flags_internal::program_usage_message = new std::string(new_usage_message);
+}
+
+// --------------------------------------------------------------------
+// Returns the usage message set by SetProgramUsageMessage().
+// Note: We able to return string_view here only because calling
+// SetProgramUsageMessage twice is prohibited.
+absl::string_view ProgramUsageMessage() {
+  absl::MutexLock l(&flags_internal::usage_message_guard);
+
+  return flags_internal::program_usage_message != nullptr
+             ? absl::string_view(*flags_internal::program_usage_message)
+             : "Warning: SetProgramUsageMessage() never called";
+}
+
+}  // namespace absl